Information source: United States Geological Survey, Western Geographic Science Center

Revision date: 2009-02-10

Scope: For small scale (1:1million and smaller) statistical mapping.

Remarks: Uses spherical projection formulae. USGS documentation describes sphere as derived from GRS80/WGS84 ellipsoid but that actually used is Clarke 1866. For 1:1million and smaller scale maps there is no significant difference.

PROJCS["US_National_Atlas_Equal_Area",GEOGCS["GCS_Unspecified datum based upon the Clarke 1866 Authalic Sphere",DATUM["D_Sphere_Clarke_1866_Authalic",SPHEROID["Clarke_1866_Authalic_Sphere",6370997,0]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Lambert_Azimuthal_Equal_Area"],PARAMETER["latitude_of_origin",45],PARAMETER["central_meridian",-100],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1]]